We have recently shown that the yeast F1F0-ATP synthase complex exists as a dimer in the mitochondrial inner membrane. Isolation of the dimeric AlP synthase complex led to the identification of three new subunits of the complex. These subunits, Su e, Su g and Su k were found to be specifically associated with the dimeric form of the ATP synthase complex. The present proposal focuses on understanding the formation and function of the ATP synthase dimer. Su e appears to play a central role in the formation of the dimeric ATP synthase. Understanding both the function and the arrangement of Su e, and the other dimer specific-subunits, within the F0-sector represents a major goal of this research proposal. Second, we wish to analyze if the dimeric form of the F1F0-ATPase complex plays a central role in its ability to be inhibited by the natural inhibitor protein, IF1. It has been recently demonstrated that the natural inhibitor protein of the ATPase, IF1 (termed INH 1 in yeast) forms dimers and binds two neighboring F1-domains, concomitantly. We shall analyze whether formation of the dimeric F1F0-ATP synthase, mediated by Su e and Su g, plays a role in maintaining neighboring F1-sectors in close proximity to each other, so as to enable binding of the inhibitor protein dimer. Finally, our preliminary data suggests that the formation of the ATP synthase dimer is important for the maximal activity of the cytochrome oxidase complex. The analysis of the role of the dimeric ATP synthase and possible involvement with the cytochrome oxidase complex is also proposed. Since the assembly and oligomeric state of both of these complexes is anticipated to be similar in all eukaryotes, information gained from these studies should be helpful in the future analysis of human disorders stemming from enzymatic deficiencies in either the F1F0-ATP synthase or cytochrome oxidase complexes.